Voltage control



July 23, 1940.

Filed Jan. 22, 1958 o n F H INVENTOR Laeelw B. Haddad flflulv v" ATTORNYs Patented July 23, 1940 UNITED STATES PATENT OFFICE VOLTAGE CONTROLApplication January 22, 1938, Serial No. 186,307

10 Claims.

This invention relates to an art and apparatus for treating materials bythe use of electricity, particularly the control of the electricity usedin such treatment.

One of the objects of this invention is to provide apparatus of durableconstruction for carrying on an electrical treatment process in anefficient and dependable manner. Another object is to provide an art andapparatus of the above character for insuring the maintenance of certainpredetermined conditions within a zone where materials are beingtreated. A further object is to provide an art and apparatus of thistype for maintaining a constant effective volt- 15 age, with variationsin the load conditions and the source of power. Other objects will be inpart obvious and in part pointed out hereinafter.

The invention accordingly consists in the features of construction,combinations of elements arrangements of parts and in the several stepsand relation and order of each of the same to one or more of the others,all as will be illustratively described herein, and the scope of theapplication of which will be indicated in the following 25 claims.

In the accompanying drawing, in which are shown several of the variouspossible embodiments of the invention:

Figure 1 is a diagrammatic representation of 36 the electrical circuitand certain of the mechanical parts of an electrical sterilizingapparatus showing one embodiment of my control system; and,

Figure 2 is a diagrammatic representation of a portion of a modifiedform of control system.

Referring to the right hand side of Figure l, illustratively, an upperelectrode structure 2 is positioned directly over a plurality ofelectrode rollers 4. Each of the electrode rollers 4 comas lowpower-factor glass, and an elongated electrode element 8 positionedwithin the dielectric shell. The electrode elements 8 comprise the lowerelectrode structure and cooperate with the upper electrode structure 2to form a treatment zone l0 therebetween. Apparatus (not shown) isprovided for rotating rollers 4, and the packages of the product beingtreated are placed upon the roller at the extreme right and pass fromone roller to another throughthe treatment zone Ill. The lower electrodestructure is connected to a ground connection 20 through a plurality ofindividual air condensers I8 and the upper electrode structure 2 isconnected to one lead l2 of the output side of a high potentialauto-transprises a hollow shell 6 of dielectric material, such former I4the other lead of which is grounded. Auto-transformer I4 is a translatorto raise the voltage of the output of alternator 22 to which it isconnected by leads 24 and 26. In this manner a high potential gradientis produced within 5 the treatment zone l0 which is normally occupied bya gaseous dielectric such as air. The dielectric properties of thepackages being treated are such that when they move into the treatmentzone displacing air, electrical discharges occur through the packagesdestroying all insect life which may exist therein, including the adult,egg, pupa and larva stages. In this treatment it is important that thehigh potential be great enough to thoroughly treat the material but atthe same time there should be no danger of spark discharges which mightinjure the packages or the product.

In some installations the amount of current flowing when packages arewithin the treatment zone is large enough to cause an appreciable loadupon the alternator 22 resulting in a reduction of its speed. Also, thesource of power, shown as a commercial three-phase circuit energizing amotor 42, might vary in frequency or voltage to change the alternatorspeed. Any change in the speed of the alternator causes a correspondingchange in its output voltage and frequency, and at the same time thereare changes in its synchronous reactance. The changes in speed alsocause changes in the field current of alternator 22 which is supplied byan exciter 46 through an adjustable rheostat 48. These changes infrequency also cause changes in the reactances of the other units in thesystem such as, auto-transformer I4 and the electrode structureincluding condensers [8. When relatively high frequencies are used thesevarious changes are appreciable, and under some conditions of operationsmall changes in alternator speed cause excessive changes in theefiective high potential.

For purposes of clarity the synchronous reactance of alternator 22 isshown separately and is designated by the numeral 40 connected in lead26. With this type of mechanism the primary current of autotransformerI4 is normally leading, having a relatively small in-phase component andan out-of-phase component leading the voltage by 90. This is due to thefact that this apparatus is normally operated at relatively highvoltages and frequencies. Under normal operating conditions there isvery little secondary current flow from auto-transformer M to theelectrodes when there are no packages within the treatment zone, butwhen a package moves into 55 the treatment zone the current flow rapidlyincreases, and the corresponding primary current is leading. Synchronousreactance 40 materiallly affects the load-voltage or regulationcharacteristics of the alternator. This is especially true due to thefact that the out-of-phase leading component of the load current, whenflowing through synchronous reactance 40, sets up a voltage which lagsthis leading current by 90, and thus is in phase with the alternatorvoltage. As a result of this, when the load current increases due to apackage moving into the treat-= ment zone, there is an increase in theoutput voltage of the alternator and this increase may be sufiicient tocause surges in the circuit and an excessive high potential gradientwithin the treament zone.

In order to avoid these undesirable effects a series condenser 28 isprovided in the circuit which has a capacitive reactance value slightlyless than the value of synchronous reactance 40 and compensates for theeffect thereof. The voltage across this condenser, resulting from the 90out-of-phase leading component of current, leads this component by 90and thus is out of phase with the alternator voltage. In this manner thevoltage across condenser'28 is directly opposed to the alternatorvoltage and the voltage caused by synchronous reactance 40.

As pointed out above, the value of condenser 28 is slightly less thanthe value of synchronous reactance 40 and, thus, the compensatingvoltage across condenser 28 is slightly less than the increase involtage caused by synchronous I650? tance 40 with the result that thereis a rise in the voltage across the input side of auto-transformer M.This rise in voltage is sufficient to compensate for the drop in voltagecaused by the resistance in the circuit. In this way the value ofcondenser 28 is such that it maintains constant voltage on the inputside of auto-transformer l4 even though there are rapid changes in theload current. Condenser 28 is also effective to limit surges in thecircuit and variations in the voltage across the input side ofauto-transformer M which might otherwise result from variations inthespeed of alternator 22.

As indicated above, auto-transformer l4 draws a leading current and inorder to maintain the line. current at a minimum, a resonance coil 38 isconnected in parallel with the primary of the auto-transformer.Resonance coil 38 draws a lagging current and its value is such that acondition of parallel resonance exists at no load and at approximatelythe normal operating frequency. Thus, at this resonant frequency, theout-of-phase lagging. current of resonance coil 38 equalstheout-of-phase leading current drawn by the auto-transformer and thecurrent flowing in leads 24 and 26 is substantially in phase with thevoltage.

The relative values of the various elements of the circuit are such thata condition of series resonance occurs between condenser 28 and thetotal equivalent inductive reactance within the circuit. This totalequivalent inductive reactance includes synchronous reactance 40 and theequivalent reactance of resonance coil 38 and autotransforme'r H inparallel and this resonance condition occurs at a frequency below-thenormal operating frequency. In order to avoid excessive voltages at thisresonance frequency when alternator 22 is being brought up to normalspeed, a shunt circuit is provided to by-pass the current aaoasva of thelower frequencies around condenser 28. This shunt circuit consists of aresistor 32 connected in series with a parallel resonant circuitcomprising a condenser 34 and an inductance 36.

The values of condenser 34 and inductance 36 are such that they are inparallel resonance at or near the operating frequency; thus, duringnormal operation, very little current flows through this shunt circuitand the action of condenser 28 is not interfered with, but at lowerfrequencies the reactance of this shunt circuit is very small andcondenser 28 is made ineffective because very 7 little current flowsthrough it. The current flowing through the shunt circuit is limited byresistor 32, but as this current is very small during normal operation,there is no great loss of power at this resistor.

- Inductance 36 is variable and may be adjusted so that resonance of theshunt circuit occurs at a frequency either above or below the normaloperating frequency. Furthermore, the value of condenser 28 with respectto synchronous reactance 40 may be such as to cause either a rising or afalling load-voltage characteristic. Thus, by fixing the values ofresonance coil 38. series condenser 28 and inductance 36, the effectiveinput voltage to auto-transformer l4, and hence the high potentialgradient within thetreatment zone is reliably controlled, and willautomatically remain within certain predetermined limits. The

apparatus may be adjusted so that the potential v gradient will eitherremain constant or vary along a predetermined curve when there arevariations in the alternator speed and load conditions.

An alternative circuit is shown in Figure 2 where condenser 58 replacescondenser 28 and is in series with a condenser 54 and an inductance 56.Condenser 54 and inductance 56 are shunted by a resistor 52. The valuesof condenser 54 and I inductance 56 are such that they are in seriesresonance at a frequency near the normal operating frequency. During thestarting period, as alternator 22 is being brought up to speed, thecircuit of condenser 54 and inductance 56 has a very high capacitivereactance and the current is shunted through resistor 52, but at thenormal operating frequency the reactance of condenser 54 and inductance56 is very small and very little current flows through resistor 52.Inductance 56 may be adjusted in the same manner as may induetance 36 soas to obtain any predetermined condition of voltage regulation.

With apparatus of this character, the frequency and voltage of the highpotential may be varied over wide'ranges depending upon the I in variousparts, all without departing from the scope of the inventiomit is to beunderstood that all matter hereinabove set forth, or shown in theaccompanying drawing is to be interpreted as illustrative and not in alimiting sense.

ing a high potential the electrical discharges resulting irom'imprcss--of a predetermined value upon an electrode structure, the combinationof,

an electrode structure positioned to define a treatment zone, a highpotential transformer having its output side connected to said electrodestructure and its input side connected to an alternator by electricalconductor means, a first condenser connected in said electricalconductor means, a first inductance connected in parallel with the inputside of said transformer, and a shunt circuit connected around saidfirst condenser including a second condenser and a second inductance inparallel, the respective values of the inductance and the capacity ofthe various elements being such that at or near the normal operatingfrequency of said apparatus said second condenser and said secondinductance are at parallel resonance and the potential gradient withinthe treatment zone is reliably regulated.

2. In electrical apparatus in which a product is treated in a treatmentzone by means of elec-' trical discharges resulting from impressing ahigh potential of predetermined value upon an electrode structure, thecombination of, an electrode structure positioned to define a treatmentzone, and an electrical circuit connected to said electrode structureincluding, an alternator, a main condenser unit connected in series withthe output of said alternator, and a condenserinductance resonance unitelectrically connected with said main condenser unit, the respectivevalues of the inductance and the capacitance of the elements being suchthat said resonance unit is in resonance at or near the normal operatingfrequency of said apparatus and the potential gradient within thetreatment zone is reliably regulated.

3. In electrical apparatus in which a product is treated in a treatmentzone by means of electrical discharges resulting from impressing a highpotential of predetermined value upon an electrode structure, thecombination of, an electrode structure positioned to define a treatmentzone, and an electrical circuit connected to said electrode structureincluding, an alternator, a main condenser unit connected in series withthe output of said alternator, and a shunt circuit connected around saidmain cendenser unit including a second condenser and an inductance inparallel, the respective values of the inductance and the capacitance ofthe elements being such that at or near the normal operating frequencyof said apparatus said second condenser and said inductance are inparallel resonance and the potential gradient within the treatment zoneis reliably regulated.

4. In electrical apparatus in which a product is treated in a treatmentzone by means of electrical discharges resulting from impressing a highpotential of predetermined value upon an electrode structure, thecombination of, an electrical structure positioned to define a treatmentzone, and an electrical circuit connected to said electrode structureincluding, an alternator, a main condenser unit connected in series withthe output of said alternator, and a resonance unit in series with saidmain condenser unit, said resonance unit comprising a second condenserand an inductance, the respective values of the inductance and thecapacitance of the elements being such that they are in series resonanceat or near the normal operating frequency and the potential gradientwithin the treatment zone is reliably regulated.

5. In electrical apparatus in which a product is treated in a treatmentzone by means of elec-' trical discharges resulting from impressing ahigh potential of predetermined value upon an electrode structure, thecombination of, an electrode structure positioned to define a treatmentzone, and an electrical circuit connected to said electrode structureincluding, an alternator, a main condenser unit connected in series withthe output of said alternator, and a control unit including a resistanceunit and a condenser-inductance resonance unit electrically connectedwith said main condenser unit, the respective values of the inductanceand the capacitance of the elements being such that said resonance unitis in resonance at or near the normal operating frequency of saidapparatus and said resistance unit being of a value to prevent an excessfiow of currentwhereby said main condenser unit is renderedsubstantially ineifective except within the normal frequency range andthe potential gradient within the treatment zone is reliably regulated.

6. In electrical apparatus in which a product is treated in a treatmentzone by means of electrical discharges resulting from impressing a highpotential of predetermined value upon an electrode structure, thecombination of, an electrode structure positioned to define a treatmentzone, and an electrical electrode structure including, an alternator, aninductance unit electrically connected in parallel with said electrodestructure, a main condenser unit connected in series with the output ofsaid alternator, and a condenser-inductance resonance unit electricallyconnected to regulate the current flowing through said main condenserunit, the respective values of the inductance and the capacitance of theelements being such that said resonance unit is in resonance at or nearthe normal operating frequency of said apparatus and the potentialgradient within the treatment zone is reliably regulated.

'7. In apparatus of the class described; the combination of analternator for producing an alternating current of substantiallyconstant voltage; treating apparatus having a pair of electrodestructures between which a high potential gradient is produced; andcircuit means connecting the output of said alternator across saidelectrode structures including, a main condenser unit connected to carrythe normal alternator output current and compensate for variations inoutput voltage due to the inductive impedance of said alternator, and afrequency-responsive current controlling unit to render said maincondenser substantially ineffective except within the normal range ofoperating frequencies, said current controlling unit including aresonance circuit connected with a resistance unit to cause the majorportion of the current flowing in the main circuit at frequencies otherthan the normal range of operating frequencies to flow through saidresistance unit and to prevent the flow of a substantial current throughsaid resistance unit during normal operation.

8. In apparatus of the class described, the combination of: analternator for producing an alternating current of substantiallyconstant voltage; treating apparatus having a pair of electrodestructures between which a high potential gradiant is produced; andcircuit means circuit connected to said connecting the output of saidalternator across said electrode structures including. a main condenserunit connected to carry the normal alternator output current andcompensate for variations in output voltage due to the inductiveimpedance of said alternator, and a frequency-responsive unit includinga resistance unit and a resonance unit connected to prevent the flow ofa substantial amount oi current through said main condenser atfrequencies other than the normal operating frequencies.

9. In apparatus of the class described, the combination of an alternatorfor producing an alternating current of substantially constant voltage;treating apparatus having a pair of electrode structures between which ahigh potential gradient is produced; and circuit means connecting theoutput of said alternator across said electrode structures including, amain condenser unit connected to carry the normal alternator outputcurrent and compensate for variations in output voltage due to theinductive impedance of said alternator, and a frequency-responsive shuntcircuit connected to .by-pass said main condenser unit, said shuntcircuit comprising a resistance unit in series with a parallel resonanceunit which is resonant at substantially the normal operating frequency.

10. In apparatus of the class described, the combination of: analternator for producing an alternating current of substantiallyconstant voltage; treating apparatus having a pair of electrodestructures between which a high. potential gradient is produced; andcircuit means connecting the output of said alternator across saidelectrode structures including, a main condenser unit connected to carrythe normal alternator output current and compensate for variations inoutput voltage due to the inductive impedance of said alternator, aresistance unit in series with said main condenser unit, and a seriesresonance circuit connected across said resistance unit and beingresonant at substantially the normal operating frequency to therebyby-pass said resistance unit during normal operation.

LABEEB B. HADDAD.

I CERTIFICATE OF CORRZC'I'ION. Patent to. 2,208,573. July 25, 191w.LABEEB B. HADDAD.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page 1,second column, line 1 6, for "autotransformer" read -autotrensformer-;page 2, first coiumn, line 3-14., for "materialily" read -materia1ly-;page 5, first column, line 65 ,claim 14, for the word "electrical" read-electrode; and that the said Letters Patent should be readwith thiscorrection therein that the same may conform to the record of the casein the Patent Office.

Signed and sealed this llLth day of January, A. D. 1910.. I

Henry Van Arsdale,

(Seal) Acting Commissioner of Patents.

